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imputation from which common candor and decency 
ought to have protected fo great a name *. 
For inftance, when he fays that “ light as often 
as by contrary refractions it is fo corrected that it e- 
mergeth in lines parallel to thofe in which it was in- 
cident, continues ever after to be white”; can this 
affertion poffibly bear the meaning they would ob- 
trude upon us ? Flad Sir Ifaac fo entirely forgot his 
own doCtrine as not to know, That if the glafs pritm 
PN», in the laft fcheme, is, any where above V v, 
terminated by a plane to which the pencil SO is per- 
pendicular, the rays V v, Rr, &c. though emerging 
parallel to SO, will exhibit their feveral colours? 
The fenfe therefore which the experiments affix to 
Sir Ifaac Newton’s words being fo abfurd, had not 
they done better to look out for one that was con- 
fident with his theory ? and fuch a one they would 
have found by only drawing a figure like the fore- 
going; where the rays of the pencil, reunited in os, 
as well as when feparated within the glafs prifm, are 
parallel to each other and to the incident pencil. But, 
if the water is terminated by a plane different from 
AC, paffing through the point o, and making the 
rays (no longer parallel to SO) to diverge, then the 
light will, by degrees, in paffing on from o, become 
coloured : which is Sir Ifaac’s other pofition. 
To this meaning his own words ought to have led 
the objeCtors. It was light, not feparate rays, which 
* The reader ought to be told, that it is not here intended to 
detract from the merit of the late Mr. Dollond’s improvement of 
refradting telefcopes ; but only to corredt a miftake of his con- 
cerning that difference of difperlion of rays, which he has fo 
happily applied to ufc. 
emerged 
